“Modulation” refers to an operation in which data is converted into a suitable form for transmission by usually carrying the data on a carrier in order to transmit information or data from one point to another point or from a first apparatus to a second apparatus through a communication line or a radio link. After received by the second apparatus, the modulated data is demodulated, that is, is restored to a suitable form to be subsequently used in the second apparatus by removing the carrier.
According to signal waves expressing information to be transmitted, such modulation includes various modulation schemes such as amplitude, frequency and time modulation schemes for a high frequency current or voltage of a sine wave, a periodic pulse or the like.
Orthogonal modulation as one of various modulation schemes is a modulation scheme using an orthogonal code in the modulation, and is characterized in that it is suitable for systems having a limitation on available power because a Signal-to-Noise Ratio (SNR) per bit required for attaining a given bit error rate goes lower as a modulation dimension increases.
When a coherent detection technology is used on a receiver side in order to restore data modulated in the orthogonal modulation scheme, this coherent detection technology has an advantage in that signal detection can be accurately made because of its relatively superior SNR characteristic, but also has a drawback in that a receiver for the coherent detection has a complicated structure and it takes a long time to fix coherence. Therefore, the coherent detection technology may be a good option when the required level of the SNR characteristic of a receiver is high in spite of its complicated structure, while it is improper when a receiver needs to have a simple structure or power consumption of the receiver needs to be small.
Meanwhile, a chirp signal is known as particularly suitable for measuring distance in a radar technology and so forth. A Surface Acoustic Wave (SAW) device is commonly used for detecting such a chirp signal. The SAW device refers to a device which propagates an elastic acoustic wave on an ultra-small sized substrate to perform a wide range of functions by using a property in which an acoustic wave propagating as an elastic acoustic wave within a crystalline solid can be produced by applying a mechanical impact on crystals or as a result of piezoelectric effects, and is used in a signal processing system.
A detection technology using this SAW device is a detection technology in which correlation values of a chirp signal are continuously derived over a time by using the SAW device on a receiver side, thereby using a point of time at which a correlation peak appears and the magnitude of the signal having the correlation peak for the detection. Although having the advantages that it has a high detection probability of the chirp signal and it detects the arrival time of the chirp signal accurately, such a detection technology also has a drawback in that the SAW device has a larger size and is rather expensive as compared with a digital semiconductor device.
Also, in order to form the whole transmitter/receiver apparatus as a System on Chip (SoC) by using a semiconductor technology, there is a need for developing a technology for detecting a chirp signal only by means of electronic circuitry without using the SAW device. With digital-type electronic circuitry being used for detecting the chirp signal, however, the detection is hard to achieve since a cross-correlation peak needs to be obtained by performing samplings at short intervals of about ¼ correlation width so as to detect the cross-correlation peak of very short width. However, when such a fast sampling frequency is used, the detection is not feasible because of an excessive amount of calculation.